Ship{3 s drive and method of operating the same

ABSTRACT

A ship&#39;&#39;s drive and a method of operating it. The drive has a prime mover which can operate at a first power output, at a higher second power output and at a highest third power output. A screw propeller is driven in rotation by the prime mover and includes several blades which are mounted on it angularly adjustable so that they can be displaced either in leeward or, optionally, in luffward direction between a first, a second, and a third position which respectively correspond to full ahead, astern and emergency full astern drive mode. A control unit is provided which couples the propeller with the prime mover in such a manner that the blades can be displaced towards the first position only in leeward direction and only when the prime mover is at its first power output. When the prime mover delivers its second power output the blades can be displaced towards the second position only in luffward direction. In case of an emergency stop, an override arrangement displaces the blades to the third position in luffward direction and irrespective of their previous position while simultaneously initiating the operation of the prime mover at its third and highest power output.

United States Patent Mades [54] ,SHIP'S DRIVE AND METHOD OF OPERATINGTHE SAME Inventor: Rudolf Mades, Brandenburgicsche Strasse 6, Berlin,30, Germany Filed: Dec.22, 1970 Appl. No.: 100,676

[30] Foreign Application Priority Data References Cited UNlTED STATESPATENTS 1/1903 Sarr ..115/34 R 3/1963 Rosen ..115/34 R X PrimaryExaminer-Milton Buchler Assistant ExaminerCarl A. Rutledge IAttorney-Michael S. Striker Dev/re {qr 9 Measuring Radar Magnet/t fieldspeed ofu um! measuring dance temperature drop [451 Sept. 26, 1972ABSTRACT A ships drive and a method of operating it. The drive has aprime mover which can operate at a first power output, at a highersecond power output and at a highest third power output. A screwpropeller is driven in rotation by the prime mover and includes severalblades which are mounted on it angularly adjustable so that they can bedisplaced either in leeward or, optionally, in lufiward directionbetween a first, a second, and a third position which respectivelycorrespond to full ahead, astern and emergency full astern drive mode. Acontrol unit is provided which couples the propeller with the primemover in such a manner that the blades can be displaced towards thefirst position only in leeward direction and only when the prime moveris at its first power output. When the prime mover delivers its secondpower output the blades can be displaced towards the second positiononly in luffward direction. In case of an emergency stop, an overridearrangement displaces the blades to the third position in luffwarddirection and irrespective of their previous position whilesimultaneously initiating the operation of the prime mover at its thirdand highest power output.

10 Claims, 2 Drawing Figures ahead 7Co/lisinn override Halo! I9L turbineQantral/er for pmpel/er fEYEfS/Ofl 2 Revers/bl? srrew propel/erHere/sing dance 29 measuring de vice PATENTED I 1 3.693.575

SHEET 1 UF 2 Device fqr g, -21:24:Quart/ 121g 9 fgg ar Magnet/Z f/E/dtemperature drop agiem 7C all/sign override kick down [(9 releasing device [onlraller for Nafur propel/er revers/on tantra/(er 2 ReversibleSE/EW propel/er lfolor ]9\ furb/ne Reversing device 29 7 Inventor;

[2149001 IMIJES SHIPS DRIVE ANDMET-HOD OF OPERATING THE SAME BACKGROUNDOF THE INVENTION The present invention is concerned with a ship's driveand with a method of operating the same.

Contrary to popular assumption, forward movement of a ship is notnecessarily its most important mode of movement. There are manyinstances whenitis equally instances where stopping maneuvers are of thegreatest importance. National and international maritime regulationsspecify, for example, which ship in certain circumstances has a right ofway; when such a situation occurs, the secondary vessel most obviouslybe capable of properly stopping its progress to avoid a collision. Thisis true in harbors, waterways and also in the open sea.

Again, it is possible that the signals of one vessel-indicating itsintended maneuver-are misunderstood by another vessel and result in abehavior of the other vessel which can lead to collision unless one orboth vessels are capable of stopping their forward movement. It ispointed out, for example, that with the state of the art prior to thepresent invention the commanding officer of a vesselis almost powerlessto avoid a collision with another, improperly maneuvering vessel once hehas taken the limited stops available to him, namely to order hisengines full astern and in order his rudder hard over.

The problems resulting from collisions with an iceberg are even worsethan those caused by collision with another vessel. Other vessels areusually recognized early enough to allow at least some evasive action;icebergs, however, are very often detected must too late to take anyeffective counteraction. This is the result of the almost invariable fogfront which develops where an icefield merges with the open sea. By thetime an approaching berg is recognized through the fog, the time anddistance available for braking the movement of the vessel by reversingits propellers is almost always too little to be of any value inavoiding a collision. This is particularly true in the case of vesselswith conventional propulsion plants and non-adjustable screw or screws,because the shortest possible stopping distance is a non-variablefunction of the propulsion plant and screw parameters.

the supply of steam or gas to the main (forward) turbine and thenstarting the secondary (reverse) turbine. However, the reverse turbinecan be started only after the main turbine is stopped-for obviousreasons-and has an output amounting to only about 60 percent of that ofthe main turbine. Moreover, in order to maintain temperature conditionswithin predetermined limits, the reverse turbine must not immediately besubjected to full load. This means that initially the secondary turbinerotates in the forward direction of the main turbine, being mounted onthe same shaft as the latter; as a result, the substantial inertia ofthe rotor of the main turbine and of the transmission gears--supportedby the turbine effect with its negative propulsion flow thrust whichdrives the propeller as a Kaplan-turbine-oppose the'desired reversal inthe direction of rotation of the shaft and propeller. It follows thatsignificant time is lost before the screw can finally exert an effectivereverse-thrust braking action. This difficulty is aggravated by the factthat in the interim period between shutting-ofi of the main turbine andthe time at which the reverse thrust of the secondary turbine becomeseffective, the vessel is left drifting with little or no response to therudder.

An example of this problem occurred recently when the supertankerManhattan attempted to open a socalled polar route to Alaska in order toprove the feasibility of exploiting the Alaskan oilfields by sea. Thevessel was intended to act as its own icebreaker and was speciallyreinforced for the purpose. It utilized a two-propeller turbine drivehaving an output of 43,000 hp at 70 rpm. However, the vessels secondaryor reverse turbine has an output amounting to only 30 percent of that ofthe main turbine. Thus, when the Manhattan became trapped in an icefieldand could become released only be reversing direction and backing out,its reverse propulsion was insufficient to free the vessel which finallyhad to be released through the efforts of two accompanying icebreakers.

One way of overcoming these problems would be to provide turbine poweredvessels with an adjustable In vessels where the propulsion plant is inform of a I reversible piston drive, such as a steam or diesel engine,the full power of the plant is available for a reversedrive maneuver.However, a non-variable (or fixed) propeller screw has an effectivenesswhich is 20 percent lower during reverse operation than during forwardoperation, owing to the reversing of the suction and pressure sides ofthe propeller as its direction of rotation is reversed. Thus, fullyeffective braking or stopping is not available even though the fullpower of the plant is.

The situation is even less advantageous where the propulsion plant is aturbine, whether it be gas-powered or steam-powered. With such apropulsion plant the braking maneuver can be initiated only by firstcutting screw propeller, so that one and the same screw (or screws ifseveral are provided) could be utilized for the reverse drive by beingpowered by the main turbine (omitting any necessity for a secondaryturbine) and by simply changing the position of the propeller bladesdepending upon whether the screws are to be set for forward or forreverse movement. However, most the the known adjustable screwpropellers have a degree of effectiveness which is approximately 4percent lower than that of fixed propellers in all operating modes, sothat consequently the operation of a turbine powered vessel usingadjustable screw propellers would be made substantially less economicalthan heretofore. These considerations account for the well known factthat adjustable screw propellers are currently in use almost exclusivelyon diesel-powered ferries which usually have to traverse comparativelyshort distances but which must almost constantly maneuver. Under suchcircumstances it is possible from an economic point of view to acceptthe lesser effectiveness of adjustable screw propellers because of theadvantage afforded by them, namely the fact that the full power of thepropulsion unit is available for reverse drive also. Of course it willbe appreciated that during reverse'operation of the adjustable screwpropeller its effectiveness is even less than during its forwardoperation because in the conventional adjustable screw propellers thepressure and suction sides of the propeller blades are necessarilyexchanged or reversed-when the propeller is adjusted for reverseoperation. It should be pointed out that conventional adjustable screwpropellers have blades which are always adjusted toward lee or in aleeward direction, meaning that-they turn through the plane of rotationof the screw. Because of the exchange of the suction and pressure sidesof the blades which is involved in this displacement, the adjustablescrew propeller which is adjusted for reverse movement hasaneffectiveness which is lower by 8 percent than even the effectivenessof the fixed propeller during the reverse operatiom The minimum loss ofeffectiveness of 4 percent in th conventional adjustable screwpropellers is caused by the very thick hub necessitated foraccommodating the control devices which control the movement of theblades between forward and reverse positions. This reduction iseffectiveness must be accepted during the entire operation of avesselprovided with such a propeller, and would thus have highly uneconomicaleffects on the fuel requirements of the vessel. For this reasonadjustable screw propellers have heretofore not been used in vesselswhich are turbine powered. Added to this is the fact that a directadjustment of the adjustable blades past their leeward position is notpossible as long as the turbine continues to operate, because when theblades reach leeward positionand before they are moved beyond it----thei1 resistance to rotation in the surrounding water drops almost tozero. Under these circumstances the turbine would run almost completelyunloaded and its revolutions per minute would increase so rapidly and sodrastically that protective devices incorporated in the turbine for thispurpose would become triggered and would shut it down. To avoid thisdifficulty it would be necessary to atleast briefly cut the supply ofthe power to the turbine and of course this also .woulddisadvantageously influence the braking operation.

It is clear, therefore, that improvements in this field are desirable,but it is equally clear that thus far they have not been forthcoming.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to overcome the aforementioned disadvantages of the prior art.

More particularly it is an object of the present invention to provide animproved ship's drive which is capable of so operating that the distancerequired for Stopping the forward movement of the vessel provided withit is drastically reduced from what is known from the prior art.

A concomitant object is to provide such an improved ship's drive inwhich the amount of propulsion power output available to the propellerof the drive during a stopping maneuver is substantially greater thanwhat is heretofore known.

An additional object of the invention is to provide an improvedmethod ofoperating such a ship s drive.

In pursuance of the above objects, and others which will become apparenthereinafter, one feature of the invention resides in a ships drivewhich, briefly stated, comprises a prime mover operable for providing afirst power output, a higher second output, anda highest third poweroutput. At least one screw propeller is mounted for rotation by theprime mover about a main axis and has a plurality of blades angularlydisplaceable about transverse pivot axis is leeward and optionally inluffward direction between at least a first, a second and a thirdposition which respectively correspond to a full ahead astern andemergency full astern .drive mode. There is further provided means whichcouples the screw propeller with the prime mover for displacement of theblades towards the first position in leeward direction when the primemover provides the first power output, from the first position towardsthe second position in luffward direction when the prime mover providesthe second power output, and to the third position in luffward directionwith concomitant operation of the prime mover at the third power output.

The invention thus provides for a necessary coupling between thecontrols for the operation of the prime mover and for the operation ofthe adjustment of the screw propeller blades. This coupling can,however, be terminated in case of a braking emergency, namely when theblades are to be moved to their third position and when simultaneouslythe prime mover is to be operated at its highest third power output.With this arrangement it is possible, according to a further concept ofthe invention, to provide a very simple and very clear control unit forcontrolling the operation of the propulsion unit, which includes boththe prime mover and the screw propeller or propellers. Such a controlunit involves a control panel provided with a single slot in which apointer moves between different positions which are indicated bysuitable indicia, such as command terminology. The pointer is moved by asingle control lever and when the control lever is moved, not only hepointer moves but also the prime mover and the blades of the screwpropeller or propellers are adjusted accordingly. When an emergencybraking action is required, an override button provided for this purposeis pushed in which case the coupling between the prime mover and thecontrol device for controlling the adjustment of the blades of the screwpropeller is terminated, and the prime mover is immediately switched toits highest power output while the blades of the screw propeller areimmediately moved in luffward direction to their reverse-propulsionposition.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specific embodimentwhen read in connection with the accompany drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagram illustrating adrive according to the present invention; and

FIG. 2 is a further diagram illustrating a control unit according o thepresent invention and also showing in symbolic form, the positioning ofthe blades of an adjustable screw propeller in the various positionswhich can be selected with the control unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT tive'of a device capable ofmeasuring the speed of a drop in the ambient temperature. The boxlabelled 9 is indicative of aradar unit and the box labelled '10 isindicative of a device for measuring the ambient magne tic field. All ofthese devices are already known in the art and need not be specificallydiscussed in detail. It will be appreciated precisely what their variousfunctions are. The manner in which they cooperate with the remainderofthe drive will be discussed subsequently.

Reference number 11 identifies a controlpanel provided with an elongatedslot 6 in which a pointer 12 is mounted for longitudinal displacement.The pointer 12 is fast with the shaft 13 of an operating lever 14 andthus will move as the latter is moved.

A scale indicating the positions astem, collision override, ahead, stopandastern isprovided adjacent the slot 6 on the control panel 11, withthe scale being generally identified with reference numeral 15 in FIG. 1and being shown in an enlarged illustration in FIG. 2. The pointer 12 ofcourse points to the respective command designation which is indicativeof the operative mode for which the ship s drive is set at the time.

The operating lever 14 is also connected in a non-illustrated mannerwith a setting device which is also not shown but which for instanceoperates on a hydraulic or an electric basis, and which controls via theconductors 16 and 17 the control device 18 for the motor turbine l9, andon the other hand the control device or controller 20 for propellerreversion which operates upon the reversing device 21 and effects theactual reversion of the blades of the reversible screw propeller 22.Thus, in any position of the control unit except operation for utilizingthe collision override mode, the devices 18 and 20 are operatedsimultaneously when the handle 14. is operated, meaning that as thepower output of the motor turbine 19 is varied via the device '18, theposition of the blades of the reversible screw propeller 22 isconcomitantly varied via the devices 20 and 21.

' If, in the event of a danger of collision the override button 7 isactuated, it acts upon the control switch 23 which may also beconsidered a kick-down releasing device to thereby disengage thecoupling of the devices 18 and 20. As the device 23 effects suchdisengagement, it at the same time switches the motor turbine 19 via themotor controller 18 to its highest power output and moves the blades ofthe reversible screw propeller 22 in luffward direction via the devices20 and 21, to their emergency full astern position.

In FIG. 2 the arrow 1 indicates the normal forward direction of a vesselprovided with the novel drive. Arrow 2 indicates the direction ofrotation of the nonillustrated and adjustable screw propeller, that isthe direction of rotation for forward movement which is indicated by thearrow 2a in FIG. 1. I

For a better understanding I have illustrated in FIG. 2 the position ofone of the adjustable blades of the screw propeller 22, and I have doneso in form of a profile. This profile is illustrated in four positionsof which the bottom position identified as astem is intended for anormal reverse drive during harbor maneuvering at low speed. The stopposition is selfevident, and the ahead position is indicativeof the fullforward movement of the vessel provided with the novel drive, it beingkept in mind that the markings 6, 8, 10, 12, 16, 20, 24 and 30 as shownin FIG. 2'are provided to indicate different degrees of forward speed.Finally, at the upper edge of FIG. 2 there is a further astern positionillustrated, showing the position of the profile of an adjustable bladeof the reversible screw propeller 22 when the vessel is to be braked atcruising speed. Of course any other desired position of the profile orprofiles can be selected continuously variable intermediate theillustrated positions,

It is clear that the pressure side of the adjustable blade which isturned from the stop position to the lowermost (in FIG. 2) asternposition, in leeward direction, is reverse whereas when the profile ismoved from ahead position to the uppermost (in FIG. 2) astern positionin leeward direction, the pressure side remains unchanged, that is thepressure side which acted during the ahead position also acts during theastern position. This provides for the previously discussed substantialincrease in the effectiveness of the novel propeller drive when theadjustment is made in luffward directions, as opposed to where theadjustment is made in leeward direction.

The terms leeward direction and luffward direction will be understood bythose versed in the art, but for purposes of greater clarity it ispointed out that when the blade is adjusted in leeward direction it ispivoted through the plane of rotation of the screw propeller, whereaswhen it is adjusted in luffward direction it is turned to astem positionthrough a position which is normal to the plane of rotation of the screwpropeller.

FIG. 2 also shows diagrammatically the crank 4 for effectingdisplacement of the blade or profile 3, and the control arm 5 for thecrank 4.

In the event of an emergency requiring emergency braking, the pushbutton7 is depressed with the results and for the purposes discussed earlier.When this is done the blades or profiles 3 move at high speed into theirmaximum reverse position and at the same time the motor turbine 19 isswitched to its maximum power output. The pushbutton may be actuatedmanually, but it can also be coupled with any or all of the devices 8, 9and 10 so that any danger detected by one of these devices can activatethe pushbutton override 7 and automatically initiate the emergencybraking procedure.

It is not believed to be necessary to discuss in detail the particularconstruction for reversible screw propellers of the type suitable foruse in the construction according to the present invention. Theconstruction of such a propeller, and of the means for adjusting itsvarious blades, it clearly disclosed in my prior US. Pat. Nos. 2,916,095and 3,122,207, as well as in German Offenlegungs schrift l 581 I29(especially in FIG. 3) to all of which reference may be had for details.Similarly, device such as the motor controller 18, the propellerreversion controller 20, the reversing device 21 and the kick-downreleasing device 23 are well-known to those skilled in the art and theirparticular construction does not in itself form a part of the presentinvention.

The reversible screw propeller disclosed in may U.S.

I Pat. No. 3,122,207 can be used with particular advantage inasmuch asits, effectiveness is greater by 4 percent than that of a fixedpropeller. When this propeller-is used in the construction according tothe present invention the total gain of effectiveness over conventionaladjustable propellers where the blades are adjusted in leewarddirections, amounts to 12 percent inasmuch as in the conventionaladjustable propellers the effectiveness is lower by 8 percent than thatof a fixed propeller.

Furthermore, the propeller disclosed in my US. Pat. No. 3,122,207, whichis of the type where the blades are adjusted'in luffwarddirection, hasthe advantage that when the blades are in luff position they act in aretarding sense and thus make it possible for the turbine to enter intothe braking maneuver at maximum power whereby the full'brakingeffectiveness is obtained immediately, by contrast to what is known fromthe art where it is necessary to at least briefly throttle the turbineto prevent itfrom turning through at non-load conditions. 7

It will be appreciated that the ships drive and methods of operationaccording to the present invention makes possible 'a completely newapproach to maneuvering in that a ships officer is now capable,beginning with the lowest ahead drive mode from which a reversal of theblades. to astern mode takes place in leeward direction, the drive canbe rapidly and continuously varied upwardly to the highest load, and atany given moment it is possible to be certain that output of theturbine, drive speedand position of the bladesare in optimumrelationship with reference to one another, whereby maximum totaleffectiveness of the propulsion unit is obtained at all times.

The lesser effectiveness of the drive when at low speed the blades areto-be moved to the reverse position in leeward direction, is acceptableunder thecircumstances because at such times the turbine operates onlyat reduced powerin any case and the losses, considered in absoluteterms, are insignificant. Also, at low speed movements it is notnecessary to obtain a drastic braking action such as is afforded byadjustment of the blades in luffward direction, because more time isavailable for stopping the vessel and because more time is available forstopping the vessel and because under these circumstances displacementof the blades in leeward direction is adequate. However, this is nottrue at higher speeds and in case of a collision danger. it is essentialto be able to utilize the full power of the propulsion unit in reverseat once, that is without any losses, which can be achieved only byreversing the blades in luffward direction according to the invention.

Moreover, the invention provides two different possibilities for brakingat high speed, and this is also important. Braking at maximum enginepower is an emergency or panic procedure which places the greateststrains upon the entire vessel and which should be used only in times ofgenuine emergency, that is for instance imminent collision. At othertimes, or when the danger of collision has not yet reached the point ofcertainty or immediacy, it should be attempted to stop the vessel byusing the screw propeller with its blades reversed in luffward directionbut with the engine output at less than fully emergency rating. Thisapproach is normally preferable because it places a lesser strain on thevessel; obviously, when an emergency braking attempt is made byoperating the override button 7, maximum strain is placed upon thevessel and may lead to damage of the engine, propeller shaft, hulland/or other components. Of course, in the case of a genuine andimminent emergency such possibilities are accepted as less dangerousthan an actual collision.

The normal braking effort is carried out at a predetermined power outputof the engine, an output which is below the maximum emergenc'y output.It is advantageous that this predetermined output-and the distancerequired for stopping the vessel under this circumstance-is determinedonce and for all before the vessel is placed into service, for instanceduring the socalledshake-down cruise. It can be determined in terms ofthat engine output of which vibrations'of the drive drain and the vesselhull-caused by the blades of the propeller in luffward displacement-donot exceed a predetermined (and acceptable) maximum. By determining inadvance the maximum braking distance required for a vessel under normalbraking operations, and under emergency braking operations, a valuabletool can be made available to the commanding officer in avoidingcollisions.

By resorting to the present invention it is possible to bring to astandstill any ship, especially any turbine ship, within a distancewhich is smaller by at least twothirds than the distance previouslyrequired. Furthermore, this can be achieved (in the case ofturbinepowered vessels) with the main turbine, whereas the need for asecondary or reverse turbine has been eliminated. Thus, the presentinvention not only provides for greater economy in the construction of avessel, but also for substantially greater safety in national andinternational navigation.

Coupling 'of the motor controller unit 18 with the propeller reversioncontrol unit 20 can be carried out in known manner and as required inindividual instances. The unit 20 advantageously uses an oil hydraulicsystem with stationary cylinders; a suitable unit may be found disclosedin my aforementionedprior patents.

The effects of an emergency braking action on the vessel, especially interms of vibrations, may be mitigated by making the drive shaft of twosections with an intermediate section being coupled to and connectingthem with one another. This is already known in this art and has atwofold purpose, namely to protect the drive shaft from bending momentsresulting from bending of the hull, and to absorb longitudinaldisplacement of the drive shaft at the axial thrust bearing for thesame.

It will be appreciated that the present invention not only provides animproved ships drive, but also a highly effective and versatile researchtool which makes it feasible to operate a vessel for study purposes inall possible drive and braking modes and under a variety ofcircumstances. This, in turn, makes it possible to determine optimumparameters for the operation of vessels of many different sizes andunder many different circumstances. The adjustable screw propeller whichis disclosed in my prior US. Pat. No. 2,916,095 is so constructed thatits blades can be adjusted through an extend of angular displacement notpossible with any of the other prior art adjustable propellers.

"propulsion system, such as a diesel engine as well as a gas turbine.For instance, the drive according to the present invention makes itpossible to adjust the blades I of the propeller even at high speed ofthe vessel, for

which purpose the wake current is utilized in an auxiliary capacity,i.e. as an aid. The effects of the wake current, and how it can beutilized in the manner just mentioned, is' fully disclosed in myearlier-mentioned prior U.s. Patents. The wake current is strongest athighest speed, so'that precisely the most abrupt meneuvernamelythe'emergency'braking action can be carried out with its aid with lowestforce requirements for adjustment of the blades of the propeller. This,incidentally, will be recognized as an important factor in special-usevessels, such as high-speed naval vessels.

It should still be pointed out that no problems exist in adapting thedrive according to the present invention to various differentdimensional and/or output requirement, so that for instance propellerdiameters as great as 9 m can be readily utilized.

It is to be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in aships drive, it is not intended to be limited to the details shown,since various modifications and structural changes may be made withoutdeparting inany way from the spirit of the present invention. I

Without further'analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalenceof the followingclaims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

1. A ship s drive, comprising in combination, a prime mover operable forproviding a first power output, a higher second power output, and ahighest third power output; at least one screw propeller mounted forrotation by said prime mover about a main axis and having a plurality ofblades angularly displaceable about transverse pivot axes in leeward andoptionally in luffward direction between at least a first, a second anda third position which respectively correspond to a full ahead, asternand emergency fully astern drive m d an means coupling said screwpropeller with said prime mover for displacement of said blades towardssaid first position in leeward direction when said prime mover providessaid first power output, from said first position towards said secondposition in luffward direction 10 Y I when said rime m ver rovides saidsecon ower output, and to said third fiosition in luffward ir ction'with concomitant operation of said prime mover at said third poweroutput.

2. A shipdrive as defined in claim 1, and means comprising a controlpanel having a slot, a pointer mounted in said slot for displacementlongitudinally of the same, indicia means on said panel spaced alongsaid slot and indicative of said first, second and third positions, andactuating means linked with said pointer and with said screw propellerand prime mover.

3. A ships drive as defined in claim 2, wherein said actuating meanscomprises an actuating member for moving said pointer between said firstand second positions, and an override member for moving said pointer tosaid'third position and for simultaneously displacing said blades tosaid third position from either of said first and second positions whileconcomitantly initiating operation of said prime mover at said thirdpower output.

4. A ships drive as defined in claim 3, said override member comprisingan override pushbutton,

5. A ships drive as defined in claim 1, said means comprising detectingmeans operable for effecting displacement of said blades to said thirdposition and concomitant operation of said prime mover at said thirdpower output in automatic response to acquisition of predeterminedinformation by said detecting means.

6. A ships drive as defined in claim 5, wherein said detecting meanscomprises a radar unit. 2

7. A ships drive as defined in claim 5, wherein said detecting meanscomprises a measuring device for measuring the speed of a drop in theambient temperature.

8. A ships drive as defined in claim 5, wherein said detecting meanscomprises a measuring device for measuring the ambient magnetic field.

9. A method of operating a ships'drive of the type having a prime moveroperable for providing a first power output, a higher second poweroutput and a highest third power output, and further having at least onescrew propeller mounted for rotation by the prime mover about a mainaxis and provided with a plurality of blades which are angularlydisplaceable about transverse pivot axes in leeward and optionally inluffward direction between at least a first, a second and a thirdposition which respectively correspond to a full ahead, astern andemergency full astern drive mode, said method comprising the steps ofdisplacing said blades towards said first position in leeward directiononly when said prime mover provides said first power output; displacingsaid blades towards said second position in luffward direction only whensaid prime mover provides said second power output; and displacing saidblades to said third position with concomitant initiation of theoperation of said prime mover at said third power output.

10. A method as defined in claim 9, wherein said ship s drive furthercomprises a detecting device for detecting predetermined information;and further comprising the step of displacing said blades to said thirdposition and operating said prime mover at said third output inautomatic response to acquisition of said predetermined information bysaid detecting device.

1. A ship''s drive, comprising in combination, a prime mover operablefor providing a first power output, a higher second power output, and ahighest third power output; at least one screw propeller mounted forrotation by said prime mover about a main axis and having a plurality ofblades angularly displaceable about transverse pivot axes in leeward andoptionally in luffward direction between at least a first, a second anda third posiTion which respectively correspond to a full ahead, asternand emergency fully astern drive mode; and means coupling said screwpropeller with said prime mover for displacement of said blades towardssaid first position in leeward direction when said prime mover providessaid first power output, from said first position towards said secondposition in luffward direction when said prime mover provides saidsecond power output, and to said third position in luffward directionwith concomitant operation of said prime mover at said third poweroutput.
 2. A ship''drive as defined in claim 1, and means comprising acontrol panel having a slot, a pointer mounted in said slot fordisplacement longitudinally of the same, indicia means on said panelspaced along said slot and indicative of said first, second and thirdpositions, and actuating means linked with said pointer and with saidscrew propeller and prime mover.
 3. A ship''s drive as defined in claim2, wherein said actuating means comprises an actuating member for movingsaid pointer between said first and second positions, and an overridemember for moving said pointer to said third position and forsimultaneously displacing said blades to said third position from eitherof said first and second positions while concomitantly initiatingoperation of said prime mover at said third power output.
 4. A ship''sdrive as defined in claim 3, said override member comprising an overridepushbutton.
 5. A ship''s drive as defined in claim 1, said meanscomprising detecting means operable for effecting displacement of saidblades to said third position and concomitant operation of said primemover at said third power output in automatic response to acquisition ofpredetermined information by said detecting means.
 6. A ship''s drive asdefined in claim 5, wherein said detecting means comprises a radar unit.7. A ship''s drive as defined in claim 5, wherein said detecting meanscomprises a measuring device for measuring the speed of a drop in theambient temperature.
 8. A ship''s drive as defined in claim 5, whereinsaid detecting means comprises a measuring device for measuring theambient magnetic field.
 9. A method of operating a ship''s drive of thetype having a prime mover operable for providing a first power output, ahigher second power output and a highest third power output, and furtherhaving at least one screw propeller mounted for rotation by the primemover about a main axis and provided with a plurality of blades whichare angularly displaceable about transverse pivot axes in leeward andoptionally in luffward direction between at least a first, a second anda third position which respectively correspond to a full ahead, asternand emergency full astern drive mode, said method comprising the stepsof displacing said blades towards said first position in leewarddirection only when said prime mover provides said first power output;displacing said blades towards said second position in luffwarddirection only when said prime mover provides said second power output;and displacing said blades to said third position with concomitantinitiation of the operation of said prime mover at said third poweroutput.
 10. A method as defined in claim 9, wherein said ship''s drivefurther comprises a detecting device for detecting predeterminedinformation; and further comprising the step of displacing said bladesto said third position and operating said prime mover at said thirdoutput in automatic response to acquisition of said predeterminedinformation by said detecting device.